In the prior art, known medical electrodes (for example ECG electrodes) for adhering to the skin of a patient consist of a support layer one side of which adheres to the skin with a recess which usually has inserted therein an electrically conducting gel (in particular embedded in a sponge). (The description “patient” naturally refers here to both males and females). The gel is in electrically conducting contact with an electrically conducting connection piece which is also often described as a sensor element or eyelet.
The connection piece can, for example, consist of a discoid base with an approximately cylindrical projection. The projection projects through a recess in the holding element while the base is bonded to the holding element. At the cylindrical projection, the connection piece is connected with an electrical conductor, for example a cable, to transmit signals from or to the electrode via an electrocardiograph, for example. One side (the side of the discoid base facing the skin) of the sensor element is in direct contact with the gel and the opposite side, i.e. the side facing away from the skin, is fixed to the holding element. The holding element can, for example, be a label and be fixed to the support.
The disadvantage with the prior art is that on bedding in the medical electrode, the electrically conducting gel between the connection piece and the holding element diffuses and thus releases the connection (for example adhesive) between the two. This deleteriously affects the function and accuracy of the electrode; under some conditions the electrode becomes completely unusable.
Thus, the aim of the present invention is to improve a medical electrode of the type defined above to improve its durability. Further, its mechanical tolerance of further operations or use is to be improved.
This aim is achieved by the features of the independent claims. The gap between the holding element and the electrically conducting connection piece (i.e. the gap between the underside of the holding element and the electrically conducting connection piece) is closed by a sealing element which is preferably ring-shaped or is sealed by the sealing element, and so the electrically conducting gel can no longer diffuse into the gap between the holding element and the connection piece or the sensor element and thus no longer release the sensor element from the holding element.
Advantageously, the sealing element is a nonwoven which is impregnated with a heat-activatable adhesive. An example of a heat-activatable adhesive is a hot melt glue which can be activated by raising the temperature and on cooling and setting of the glue produces a solid and functional connection. Particularly in the case of stepwise operation, such a nonwoven impregnated with heat-activatable adhesive is advantageous (as will be described below in more detail), as such a heat-activatable adhesive can be heated up and thus made manipulatable a plurality of times.
The best results have been obtained when the sensor element is completely covered with a conducting surface, preferably Ag/AgCl; it is also preferable for the plastifiable base of the sensor element to contain ABS, and for the sensor element to contain carbon fibres in an amount of less than 30%, preferably about 20%.
In a cheaper alternative, the sealing element is a thermoplastic film which plasticizes on heating so that a seal is produced after the film sets on cooling.